The present invention generally relates to articles that are made of photochromic compounds. More specifically, the present invention relates to articles that are made of photochromic chromene derivatives.
Photochromism generally concerns the ability of a compound to reversibly change color under different light conditions. One particular type of photochromic phenomenon concerns the reversible change in color of a photochromic compound from an original color to a different color when the compound is exposed to a source of ultraviolet radiation, such as solar radiation or light radiated from a mercury or xenon lamp. Of course, the original color may in fact be a colorless state. The photochromic compound fades to the original color, or the colorless state, within a period of time after the compound is isolated from the ultraviolet radiation, such as by placing the compound in a dark room.
Each particular photochromic compound has a particular set of definitive characteristics. There is a need for the invention and development of additional photochromic compounds, since the existing photochromic compounds do not satisfactorily address consumer desires for articles incorporating photochromic compounds having particular characteristics.
One characteristic of a particular photochromic compound is the ability, or inability, to reversibly change color. A number of other characteristics relate to the color change characteristic. Some of these other characteristics include the color the compound changes to; the attributes of the color, such as the hue, lightness, and saturation of the color; the rate at which the color change occurs; and the rate at which the compound reverts to the original color from the different color, if the color change is reversible. A number of variables may affect these color and rate characteristics, including the temperature of the compound, whether or not the compound is incorporated into a matrix or a solution, the characteristics of the matrix or solution, and the light conditions the compound is exposed to, including the presence or absence of light, the wavelength of the light, and the intensity of the light. The light conditions also impact another characteristic relating to the color change characteristic, the effect of mixtures of light wavelengths of the same or different intensities on the color the compound changes to and on the stability of the color the compound changes to.
Various products, including optical lenses, incorporate the principal of photochromism. For example, photochromic compounds, such as naphthopyrans, are incorporated into matrices, such as plastic ophthalmic lenses, to effect color changes in the lenses when the lenses are exposed to particular lighting conditions. Additionally, different photochromic compounds may be blended to create a color effect that is different from the respective color effects of the individual photochromic compounds. As an example, a first photochromic compound that turns orange or red when activated by light and a second photochromic compound that turns blue when activated by light may be blended to form a photochromic mixture that produces a shade of gray when activated by light.
Several types of photochromic compounds have been reported which exhibit changes in color when exposed to ultraviolet light. One particular class of photochromic compounds includes chromene derivatives, such as the 3,3-disubstituted naphthopyrans. One specific group of 3,3-disubstituted naphthopyrans includes the 3H-naphtho[2,1b]pyrans. The color response of the 3H-naphtho[2,1b]pyrans to ultraviolet light extends to purple, red, orange or yellow, depending upon the composition and structure of the particular 3H-naphtho[2,1b]pyran and the ambient conditions, such as temperature and light conditions. A general expression of the 3H-naphtho[2,1b]pyrans is provided in graphical formula I: ##STR2## where R.sub.1 and R.sub.2 are substituents attached to the pyran ring at the position indicated.
Several photochromic compounds are described in U.S. Pat. No. 3,567,605 to Becker. The Becker patent describes various chromenes and chromene derivatives that are photochromic at relatively low temperatures, such as temperatures below about -40.degree. C. These chromene derivatives are not useful for incorporation into ophthalmic lenses since ophthalmic lenses are typically worn at temperatures much warmer than -40.degree. C. The Becker patent also describes chromenes and chromene derivatives which are photochromic at room temperature, such as diphenyl-3H-naphtho[2,1b]pyran, where R.sub.1 and R.sub.2 of formula I are each unsubstituted phenyl groups.
Additional photochromic compounds are described in U.S. Pat. No. 4,931,221 to Heller et al. One type of photochromic compound described in Heller generally has the form of graphical formula I with R.sub.1 and R.sub.2 being cyclopropyl radicals and with any of various substituents included on the naphtho portion of the naphthopyran rings. Heller reports a larger bathochromic shift in the visible spectrum of 3H-naphtho[2,1b]pyrans that include the cyclopropyl radicals, as compared to 3H-naphtho[2,1b]pyrans that include alkyl groups or a spirocycloalkyl group in place of the cyclopropyl radicals.
Other photochromic compounds are described in U.S. Pat. No. 5,066,818 to Gemert et al. One photochromic compound class described in Gemert generally meets graphical formula I with one of R.sub.1 and R.sub.2 being a substituted phenyl radical, with one of R.sub.1 and R.sub.2 being either a substituted or unsubstituted phenyl radical, and with various substituents included on the naphtho portion of the naphthopyran rings. Gemert lists various non-aryl groups as potential substituents of the phenyl radicals of R.sub.1 and R.sub.2. Gemert reports a range of decolorization rates associated with the 3H-naphtho[2,1b]pyrans that include the phenyl radicals as R.sub.1 and R.sub.2.
Additional photochromic compounds are described in U.S. Pat. No. 5,106,998 to Tanaka et al. Tanaka describes compounds in which R.sub.1 and R.sub.2 of graphical formula I are alkyl groups. Tanaka reports several fade times and maximum absorption wavelengths associated with various 3H-naphtho[2,1b]pyrans that include the alkyl radicals as R.sub.1 and R.sub.2 in formula I.
U.S. Pat. No. 5,238,981 to Knowles teaches a 3H-naphtho[2,1b]pyran compound in which R.sub.1 and R.sub.2 of graphical formula I are each selected from a group of organic radicals that includes phenyl and naphthyl. The organic radicals placed at R.sub.1 and R.sub.2 are either substituted or unsubstituted. Potential substituents of substituted organic radicals placed at R.sub.1 and R.sub.2, provided that one of the organic radicals placed at R.sub.1 and R.sub.2 is a phenyl group, include various non-aryl groups. Various potential substitutions on the naphtho portion of the naphthopyran ring are taught, including an 8-methoxy substitution. Knowles states that the number eight carbon atom substitutions, such as the 8-methoxy substitution, cause a bathochromic shift in the visible spectrum associated with activated forms of the 3H-naphtho[2,1b]pyrans and in the ultraviolet spectrum of unactivated forms of the 3H-naphtho[2,1b]pyrans.
Additional photochromic compounds are described in U.S. Pat. No. 5,244,602 to Van Gemert. Van Gemert describes 3H-naphtho[2,1b]pyrans in which R.sub.1 and R.sub.2 of graphical formula I are each phenyl, naphthyl, various heterocyclic groups, and certain non-aryl groups. Van Gemert also discusses substitution of various non-aryl substituents into any phenyl, naphthyl, heterocyclic, and non-aryl groups placed at R.sub.1 and R.sub.2. Van Gemert also states that certain substitutions at the number 5 carbon on the naphtho ring causes a bathochromic shift of the absorption maximum of the 3H-naphtho[2,1b]pyrans.
U.S. Pat. No. 5,274,132 to Van Gemert describes certain 3H-naphtho[2,1b]pyrans in which R.sub.1 of graphical formula I is a phenyl group, a naphthyl group, a furyl group, or a thienyl group and in which R.sub.2 of graphical formula I is an arylalkenyl radical. Van Gemert describes a bathochromic shift associated with the 3H-naphtho[2,1b]pyrans that include the arylalkenyl radical, relative to certain other naphthopyrans disclosed in U.S. Pat. No. 3,567,605.
Other photochromic compounds are described in U.S. Pat. No. 4,685,783 to Heller et al., U.S. Pat. No. 4,882,438 to Tanaka et al., U.S. Pat. No. 5,055,576 to Castaldi, and U.S. Pat. No. 5,242,624 to Malatesta et al. Other photochromic compounds that are derivatives of chromene are described in U.S. Pat. No. 4,818,096 to Heller et al., U.S. Pat. No. 4,826,977 to Heller et al., and U.S. Pat. No. 4,990,287 to Bennion et al.
Though a number of photochromic compounds with particular characteristics have been identified, the characteristics of any particular one of these compounds do not meet all demands of current consumers. Thus, there is a need for the invention and development of additional photochromic compounds that address changing consumer desires for articles incorporating photochromic compounds having particular characteristics.